The case with sparking is probably a real problem that should be handled carefully. I'd assume in whatever powers the mic.
Everything else, you're probably just measuring expected leakage current through Y caps and whatnot, in certain scenarios (e.g. barefoot on earth or a bare concrete floor) that little current can be felt. Remember that it does not take much current to generate a voltage across the 10 megaohm input impedence of a typical DMM, in fact you can use that resistance as a current shunt in a pinch, 1 volt=100 nano amps (0.1 uA). Takes a "low impedence" meter, or a light bulb, to see if there's any hazardous current available, this is why electrician oriented enters usually have such a mode, or outright make all voltage measurements low z.